NON-INVASIVE PRENATAL SCREENING
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ProCrea’s Harmony Test, with a prenatal non-invasive test, looks for trisomies 21, 18, 13, X, Y and determines the sex of the unborn child. This test allows identification of any chromosomal anomalies the child may have and is completely risk-free for the child. The test is carried out by ProcreaLab, the laboratory that specialises in molecular genetics present in our medical centre. The test has a very high accuracy rate in terms of sensitivity and specificity. This is due to the continuous validation made possible by its huge global success: with more than 500,000 women analysed since its introduction in 2012,
Harmony™ is the most widely used test in the world. The test is performed from the tenth week of pregnancy, even in twin pregnancies, in pregnancies from assisted fertilisation and in egg donation pregnancies. The result is obtained in about a week.
What is chromosomal aneuploidy?
What Trisomy is and how it can be generated
The inherited material (DNA) in cells of the human body is organized into structures called chromosomes. Every time the cell divides the number of chromosomes doubles and divides into two daughter cells. Mistakes can happen during this process. If these mistakes occur during gamete formation, egg and sperm cells, and these gametes generate a child, the offspring will inherit the mistake. Many mistakes in the genetic patrimony spontaneously end the pregnancy very early. The most common mistake in terms of chromosomal number is trisomy 21, where chromosome 21 is present in three pairs, instead of two, in every cell. Trisomy of chromosome 21 causes Down syndrome.
More rarely, the trisomy can affect chromosome 18 (Edwards syndrome) or chromosome 13 (Patau syndrome). Both cause severe malformations, mental and psychomotor retardation. Because of their severity, only a small number of affected foetuses reach full term of the pregnancy.
How can these trisomies be detected during pregnancy??
There are invasive and non-invasive screening techniques before birth.
Non-invasive techniques are ultrasound and screening the mother’s blood: the measurement of the nuchal translucency during the first trimester, for example.
The risk that a foetus might have trisomy 21 can be calculated through these non-invasive methods, but a certain diagnosis cannot be formulated.
An invasive technique is one that penetrates into the pregnant woman’s body to collect foetal material; amniocentesis and chorionic villus sampling are invasive techniques.
Foetal cells are collected in both cases. These techniques can give certain results, but they involve the risk of spontaneous abortion (0.2-1%).
New non-invasive techniques, such as the Harmony™ test, which are based on free foetal DNA quantification present in the mother’s blood during pregnancy, make it possible to screen for the most common forms of foetal trisomies 21, 18 and 13, with a very high sensitivity, the so-called free trisomies, and they are absolutely risk-free for the foetus. This technique involves blood collection, which is absolutely safe for the foetus.
Limits of the test
Most pregnancies end with the birth of a healthy baby. This may be not true in a small percentage, unfortunately.
Nowadays many diseases can be diagnosed during pregnancy. Despite that, all known disease cannot be excluded. No one can guarantee you will have a healthy baby.
Thanks to non-invasive testing, it is possible to screen for the presence of the most common trisomies (21, 18, 13 and numeric abnormalities of chromosomes X and Y) with great accuracy. All other chromosomal abnormalities cannot be diagnosed with these non-invasive tests.
Trisomy 21 is the most common chromosomal abnormality in live births. In fact, all other chromosomal abnormalities put together have the same incidence as trisomy 21 alone.
Furthermore, some rare forms of trisomy 21, 18 and 13 cannot be diagnosed. These forms are caused by the presence in 3 pairs of only part of chromosome 21, 18 or 13, or by the presence of 3 chromosomes in only part of body cells (mosaicism).
In some cases, despite accurate testing, an unclear result can be obtained. In that case another blood sample will be requested to repeat the test.
How does the test work?
After being informed in detail by the doctor and having chosen the test best suited to your needs, about20 mL of blood will be drawn. The blood will be sent to the laboratory performing the analysis (Ariosa Diagnostic, California, USA) and the result will be communicated to your doctor within 10 working days (Mon-Fri).
The cost of the test is currently not reimbursable by health insurance in Switzerland.
What happens if the result of the test is negative?
A negative result means that a trisomy 21, 18 or 13 in your foetus can be excluded with a very high probability. Despite that, it is up to the doctor who recommended the test to decide whether more testing is needed based on your clinical data.
What happens if the result of the test is positive?
A positive result for the three trisomies means there is a high probability that your foetus has trisomy 21, 18 or 13. In this case genetic consulting and confirmation of the result through invasive testing, usually amniocentesis, is highly recommended.
Please consider the following points:
Most prenatal testing has a negative result and therefore merely dispels fear and anxiety and helps foster a calm pregnancy.
If, however, foetal abnormalities are found, this can cause insecurity and conflict that can be hard to handle. Your doctor can inform you and support you. Furthermore, psychological support is recommended in these cases. Your doctor can inform you about this too.
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